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Equal volumes of following solutions are mixed, in which case the pH of  resulting solution will be average value of pH of two solutions. 
  • a)
    pH = 2 HCl     and pH = 12 NaOH
  • b)
    pH = 2 HCl and pH = 4 HCl 
  • c)
    pH = 2 HCN and pH = 12 NaOH (Ka of HCN = 10–10)    
  • d)
    pH = 5 CH3COOH and  pH = 9 NH3(aq),  Ka (CH3COOH) = Kb (NH3(aq)
Correct answer is option 'A,D'. Can you explain this answer?
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Equal volumes of following solutions are mixed, in which case the pH o...
(D) pH = 5 CH3COOH and pH = 9 NH3 (aq), both must be of equal concentrations as pKa = pKb. Hence pH = pOH only if concentrations are equal so on mixing equal volume we will get CH3COONH4 salt solution and its pH is given is given by 
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Equal volumes of following solutions are mixed, in which case the pH o...
A) pH = 2 HCl and pH = 12 NaOH:

HCl is a strong acid and completely dissociates in water to form H+ and Cl- ions. NaOH is a strong base and completely dissociates in water to form Na+ and OH- ions. When equal volumes of these solutions are mixed, the H+ and OH- ions react to form water, leaving behind Na+ and Cl- ions in the solution. Since NaCl is a salt and does not undergo further dissociation, the resulting solution will be neutral with a pH of 7.

b) pH = 2 HCl and pH = 4 HCl:

Both solutions contain HCl, which is a strong acid. When equal volumes of these solutions are mixed, the resulting solution will still contain HCl and have a pH lower than 4.

c) pH = 2 HCN and pH = 12 NaOH (Ka of HCN = 10^-9.2):

HCN is a weak acid and does not completely dissociate in water. NaOH is a strong base and completely dissociates in water to form Na+ and OH- ions. When equal volumes of these solutions are mixed, the OH- ions react with the HCN molecules to form CN- ions and water. The resulting solution will be basic since the concentration of OH- ions is higher than the concentration of H+ ions. To calculate the pH of the resulting solution, we need to find the concentration of CN- ions.

HCN + OH- → CN- + H2O

At equilibrium, the following expression holds true:

Ka = [H+][CN-]/[HCN]

Since the solution is at equilibrium, the concentration of CN- ions is equal to the concentration of HCN molecules that have reacted with OH- ions. Let x be the concentration of CN- ions in the resulting solution. Then, the concentration of HCN molecules that have reacted with OH- ions is also x.

Ka = [H+][CN-]/[HCN]

10^-9.2 = x^2/(0.5-x)

Assuming x is much smaller than 0.5, we can simplify the expression:

10^-9.2 = x^2/0.5

x = 1.4 x 10^-5 M

The concentration of OH- ions in the resulting solution is also 1.4 x 10^-5 M. Therefore, the pOH of the resulting solution is:

pOH = -log(1.4 x 10^-5) = 4.85

The pH of the resulting solution can be calculated using the following equation:

pH + pOH = 14

pH = 14 - 4.85 = 9.15

Therefore, the pH of the resulting solution will be 9.15, which is the average value of the pH of the two solutions.
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Equal volumes of following solutions are mixed, in which case the pH of resulting solution will be average value of pH of two solutions.a)pH = 2 HCl and pH = 12 NaOHb)pH = 2 HCl and pH = 4 HClc)pH = 2 HCN and pH = 12 NaOH (Ka of HCN = 10–10) d)pH = 5 CH3COOH and pH = 9 NH3(aq), Ka (CH3COOH) = Kb (NH3(aq))Correct answer is option 'A,D'. Can you explain this answer?
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